Starting and operating circuit for discharge lamps



July 2, 1963 E. LEMMERS 3,096,464

STARTING AND OPERATING CIRCUIT FOR DISCHARGE LAMPS Filed April 25, 1961.i'ill J/ 9 [J2 5/ z P/ a L3 a CZ E 2.- P2 2 I 5 OOH J3 F igZ D/ c/Irv/an hor Eugene L mmevs Jog 6 His A lr tow-neg Unite rates Patent'Ofl'ice 3,696,4fi4 Patented July 2, 1963 3,096,464 STARTING ANDOPERATING CIRCUIT FOR DISCHARGE LAMPS Eugene Lemmers, Cleveland Heights,Ohio, assignor to General Electric Company, a corporation of New YorkFiled Apr. 25, 1961, Ser. No. 105,502 9 Claims. (Cl. 315-105) Thisinvention relates to an improved starting and current regulating circuitusing a rectifier-capacitor bridge for operating discharge lamps onrectified alternating current at high efiiciency.

In copending application Serial No. 105,508 of William H. Lake, filed ofeven date herewith, entitled Discharge Lamp Ballasting Circuit, andassigned to the same assignee as the present invention, there isdisclosed a new type of ballast for electric discharge lamps which istermed a rectifier-capacitor bridge ballast. The rectifiercapacitorbridge is somewhat similar in its wiring configuration to thevoltage-doubler circuit heretofore used in electronic equipment as alow-cost transformer-less direct current power supply of low-currentcapacity. When the rectifier-capacitor bridge is used as a ballastingcircuit, the discharge lamp operates on unidirectional rectifiedcurrent, preferably having a high ripple factor, and current flowthrough the lamp results not only from the discharging but also from thecharging the capacitors of the bridge. The lamp current has a verypronounced alternating component having a fundamental frequency of twicethe line frequency superimposed on the unidirectional component, and thepolarity of the voltages across the capacitors reverses cyclically atline frequency. In the preferred mode of operation according to the Lakeinvention, the energy stored in the capacitors of the bridge by theinput voltage is transferred with high efiiciency to the lamp load, suchbeing made possible because the discharge lamp provides a load operablein two different impedance states with a voltage-sensitive transitionpoint.

A problem present in any discharge lamp operating circuit but found inaggravated form in the rectifier-capacitor bridge ballasting circuit isthat of initially starting or striking the discharge lamps. Inalternating current circuits, use is frequently made of a capacitivestarting means as a conductive strip or coating on the lamp envelope, ora metal member extending the length of the lamp and which may be builtinto the fixture, to facilitate starting. Due to the use of alternatingcurrent, capacitive charging currents then flow from one or the other ofthe lamp electrodes to the capacitive member and cause the initialionization in the lamp which gradually increases and builds up into thefull discharge. However when di-rect or unidirectional current is used,the capacitive effect is substantially limited to the first onrush ofcharging current and this is ordinarily insufficient to start the lamp.This problem is particularly pronounced where it is desired to operatetwo fluorescent lamps in series from a single rectifier-capacitor bridgeballast circuit and the bridge is operating near the upper limit of itsvoltage capacity in respect of a given source volt- The object of theinvention is to provide a convenient and economical starting circuit inconjunction with a rectifier-capacitor bridge ballasting circuit for apair of series connected discharge lamps.

A feature of the circuit in accordance with the invention is that itallows use of a capacitive starting member extending along the lamps andplaced at ground potential whereby it may be an integral part of thefixture.

In accordance with the invention, in a rectifier-capacitor bridgeballasting circuit wherein a pair of discharge lamps are connected inseries across the output junctions of the bridge, an alternating voltagerelative to ground is applied to the junction of the two lamps. In oneembodiment, a transformer is provided having a high reactancelow-current winding which is connected to supply a relatively high A.C.voltage to the junction point of the two lamps. Since the lamps operateon unidirectional current, the junction point will consist of theconnection of the cathode of one lamp to the anode of the other.Preferably a grounded capacitive member extends along the lamps in closeproximity thereto and where a metal fixture is used, the reflector ofthe fixture may suffice for this purpose. The application of A.C.voltage to the junction of the two lamps causes capacitive chargingcurernts to flow through at least one of them in conjunction with thecapacitive starting member, whereby that lamp becomes ionized and thevoltage drop across it is redcued to the point where the bridge canstart both lamps and thereafter operate in normal fashion.

In another embodiment suitable for shorter or lower voltage lamps, thejunction point of the two lamps may merely by connected to the high(ungrounded) side of the A.C. supply through a current limitingimpedance.

For further objects and advantages of the circuit according to theinvention, attention is now directed to the following description ofpreferred embodiments taken in conjunction with the accompanyingdrawing. The features of the invention believed to be novel will be moreparticularly pointed out in the appended claims.

In the drawing, wherein like reference symbols denote correspondingelements in both figures:

FIG. 1 is a schematic diagram of a rectifier-capacitor bridge ballastingcircuit for operating two discharge lamps in series and incorporatingstarting circuit means in accordance with the invention.

FIG. 2 is a schematic diagram of a variant suitable for lower voltagelamps.

Referring to the drawing, the specific circuit illustrated is intendedto operate a pair of 8 ft. long fluorescent lamps P1, P2 from a 240volt, 60 cycle A.C. line voltage applied to input terminals S1, S2. Thelamps may be conventional fluorescent lamps with filamentary activatedcathodes at both ends for supporting an electric discharge throughmercury vapor at a low pressure. However since the lamps operate onunidirectional current, cathodes are in fact needed at one end only asindicated at 1, 1' and a simple conductor such as a metal disc may beprovided for the anodes 2, 2 at the other end. Where commerciallyavailable fluorescent lamps having filamentary electrodes at both endsare used, the electrodes serving as anodes are not provided with heatingcircuits. Also, by using suitably high voltages to start the lamps as ininstant start type operation, electrode preheat may be dispensed withaltogether.

The rectifier-capacitor bridge proper is formed of two branches eachcomprising a rectifier and a capacitor connected in series between inputjunction points, the rectifiers being poled for conduction in oppositedirections. The rectifiers are preferably high efiiciencysemi-conductive diodes such as silicon diodes, and the capacitors are ofa type capable of withstanding A.C. As illustrated, the line terminalsS1, S2 are connected respectively to input junction jl, '2 of thebridge; one branch of the bridge comprises diode D1 and capacitor C1wherein D1 is poled to permit current flow from junction jl; the otherbranch comprises diode D2 and capacitor C2 wherein diode D2 is poled topermit current flow towards junction '1. In addition the first branchincludes an inductor L2 connected in series between junction '1 anddiode D1, and the second branch includes an inductor L3 connected inseries between junction '1 and diode D2. The purpose of inductors L2, L3is to cause additional voltage to be stored in capacitors C1, C2

whereby to increase the dynamic transformation ratio and the effectiveoutput voltage of the bridge circuit. The increase in output voltagewhich the bridge applies across the lamps by reason of the presence ofinductors L2, L3 is in some respects similar to an increase in the inputline voltage and makes possible the operation of longer lamps, or lampshaving a higher operating voltage, from the same line voltage supply orA.C. source. With a higher supply voltage or with shorter lamps on thesame supply voltage, inductors L2, L3 could be eliminated.

T re junction points of the diode and capacitor in each branch, namely'3 and i4, form the output points across which the utilization or loadcircuit is connected. The load circuit comprises the load properconsisting of two lamps P1, P2 connected in series with an inductor L1.In actual practice, the ballast combination is provided with terminalsor lamp holders for accommodation of the lamps in the usual way.Inductor L1 serves to limit the rate of change of current through thelamps and is made necessary by the negative impedance characteristic ofthe lamps in their high conduction state. The value of inductor L1 is adominant factor in determining the mode of operation and performance ofthe circuit. Its value is preferably selected, in accordance with theteachings of the aforementioned Lake application, to achieve operationof the discharge lamps with a bimodal impedance variation occurring attwice the frequency of the line supply voltage.

The circuit combination includes a transformer 3 provided with a primarywinding 4, a pair of low voltage center-tapped secondary windings 5, 6,and a relatively high voltage high reactance auxiliary secondary winding7. Primary winding 4 is connected across line terminal-s S1, S2,terminal S2 being the low or grounded side of the A.C. supply. Secondarywindings 5 and 6 are connected to supply preheating current to cathodes1 and 1' respectively. The center tap (or either side) of secondaryWinding 5 is connected to junction point '4 of the bridge whereby theoperating or high current load circuit is complete across outputterminals i3, i4 and includes the two lamps in series with inductor L1.Auxiliary winding 7 has one end connected to the high or ungrounded sideof the line and the other end connected to the center tap (or eitherside) of secondary winding 6 whereby it is effectively connected to thejunction point j5 of the two lamps. Thus the line voltage and thevoltage of auxiliary winding 7 are effectively added in series relativeto ground for application to the lamp junction. The capacitive startingmeans indicated at 8, 8' may consist of conductive strips or coatings onthe lamp envelopes. More conveniently, in the present instance, it mayconsist of a metal member extending the length of the lamps in closeproximity thereto, that is at a distance not exceeding approximately aninch, and where a metal fixture is used, it may be merely the metalreflector or front conductive plate of the fixture. The capacitivestarting members 8, 8 are [grounded as indicated, the object of coursebeing to place them at the same potential as the low or grounded side ofthe line.

In the operation of the circuit, capacitors C1, C2 initia'lly charge inseries to twice the peak A.C. line voltage, but this by itself would beinsufficient to start the two lamps P1, P2 in series. However analternating potential is simultaneously applied to cathode 1 of lamp P1and to anode 2. of lamp P2 which consists of the sum of the line voltageplus the A.C. voltage generated in winding 7. This voltage issufliciently high, relative to the grounded capactive starting member 8,that the changing currents flowing from cathode 1 in lamp P1 produceionization in that lamp. After lamp P1 has ionized, the voltage dropacross it is reduced and the voltage generated by the bridge is thensufiicient to ionize lamp P2 whereupon normal operation ensues with theload current flowing through both lamps in series. During normaloperation, winding 7 need not supply any current and therefore it isarranged as a high reactance winding in order to avoid incurringexcessive losses. Alternatively or in addition, a high impedance may beconnected in series with it.

Where it is desired to operate from a lower voltage supply such as avolt, 60 cycle A.C. supply, an autotransformer may be used to step upthe line voltage applied to the bridge. In such case, the windings oftransformer 3 may conveniently be combined into the autotransfor'mer sothat a single primary winding is used, and the line terminals would beapplied to terminal S2 as before, and to terminal S3 tapped into anintermediate point in primary winding 4.

A variant of the invention suitable for starting and operating shorterfluorescent lamps having lower starting and operating voltages isillustrated in FIG. 2. Lamps P1, P2 are here shown as conventionalfluorescent lamps having filamentary electrodes at both ends. But onlyelectrodes 1, 1 serving as cathodes are preheated; electrodes 9, 9'serving as anodes are not preheated and their respective lead wires maybe short-circuited. The operating voltage requirements make inductancesL2, L3 unnecessary and they are eliminated from the circuit. Thestarting voltage requirements are met by applying to the common lampjunction 1'5 merely the line voltage so that an A.C. potentialdifference equal thereto is developed between cathode 1 of lamp P1 (oranode 9' of lamp P2) and the starting members 8, 8'. This isaccomplished by connecting the high (ungrounded) side of the line atterminal S3 to one side of heater winding 6 through a current limitingresistance, suitably a resistor R1 as shown, or alternatively a smallcapacitor. The resistor does not carry appreciable current after thelamps have started and maybe of low wattage rating, for instance 1 watt.With this arrangement transformer 3 requires only the cathode heatingwindings 5, 6. Where lamps that do not require electrode preheating areused, transformer 3 may be eliminated altogether, and resistor R1 wouldthen simply be connected from the high line terminal to the common lampjunction.

By way of illustrative example of the invention, a circuit constructedin accordance with FIG. 1 of the drawing has operated under test a pairof 8 long, 200 watt configurated fluorescent lamps, commonly designated96PG17 (Power Groove) on a line supply voltage of 240 volts, 60 cyclesA.C. The following values of circuit elements were used: for L1, 0.0-7henry; for L2 and L3, 0.04 henry each; for C1 and C2, 15 microfaradseach (330 volt peak A.C.). Secondary winding 7 of transformer 3 provided320 volts R.M.S. to the junction of the two lamps measured from ground.The secondary windings S, 6 each provided 3.5 volts to the lampcathodes. The circuit started the lamps readily and operated them atrating without noticeable flicker. The voltage, current and power perlamp were respectively 158 volts, 1.6 amperes, and 208 watts; lightoutput per lamp was approximately 14,000 lumens. The total powerconsumed from the line was 446 watts and the ballast loss was 26 watts,the ballast efiiciency being 94%. The over-all efficiency of the systemwas 63 lumens per watt input from the line terminals, an efiiciencybetter than that obtainable with the usual inductive ballast.

While a specific embodiment of the invention has been illustrated anddescribed in detail, .it is intended as illustrative and not in order tolimit the invention thereto. Modifications will readily occur to thoseskilled in the art and it is intended by the appended claims to coverany such as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An operating and starting circuit for a pair of electric dischargedevices comprising input terminals for alternating current energization,a rectifier-capacitor bridge having a pair of branches connected acrosssaid input terminals, each branch including a rectifier and a capacitorconnected in series, the junction points of the rectifier and capacitorin each branch forming output junctions, a

utilization circuit comprising a pair of electric discharge devicesconnected in series across said output junctions, and high impedancemeans supplying an alternating voltage to the common junction of theelectrodes in said devices in order to ignite them.

2. An operating and starting circuit for a pair of electric dischargedevices comprising input terminals for alt-ernating currentenergization, a rectifier-capacitor bridge having a pair of branchesconnected across said input terminals, each branch including a rectifierand a capacitor connected in series, the junction points of therectifier and capacitor in each branch forming output junctions, autilization circuit comprising a pair of electric discharge devicesconnected in series across said output junctions, high impedance meanssupplying an alternating voltage to the common junction of theelectrodes in said devices in order to ignite them, and groundedcapacitive means extending along said devices in close proximitythereto.

3. An operating and starting circuit for a pair of electric dischargedevices comprising input terminals for alternating current energization,a rectifier-capacitor bridge having a pair of branches connected acrosssaid input terminals, each branch including a rectifier and a capacitorconnected in series, the junction points of the rectifier and capacitorin each branch forming output junctions, a utilization circuitcomprising a pair of electric discharge devices connected in seriesacross said output junctions, and transforming means having a primarywinding connected across said input terminals and a low current capacitysecondary winding connected to the common junction of the electrodes insaid devices to supply an alternating voltage thereto whereby to ignitesaid devices.

4. An operating and starting circuit for a pair of electric dischargedevices comprising a pair of input terminals for alternating currentenergization, a rectifiercapacitor bridge having a pair of branchesconnected across said input terminals, each branch including a rectifierand a capacitor connected in series, the junction points of therectifier and capacitor in each branch forming output junctions, autilization circuit comprising a pair of electric discharge devicesconnected in series across said output junctions, a transformer having aprimary winding connected across said input terminals, a pair ofsecondary low voltage windings in said transformer each connected to theelectrode of one of said devices operating as cathode and supplyingpreheating current thereto, an auxiliary relatively high voltage lowcurrent capacity secondary winding in said transformer, and a connectionfrom said auxiliary winding to the junction of the electrodes in saiddevices to supply an alternating voltage thereto whereby to ignite saiddevices.

5. An operating and starting circuit for a pair of electric dischargedevices comprising low and high input terminals for alternating currentenergization, a rectifiercapacitor bridge having a pair of branchesconnected across said input terminals, each branch including a rectifierand a capacitor connected in series, the junction points of therectifier and capacitor in each branch forming output junctions, autilization circuit comprising an inductance and a pair of electricdischarge devices connected in series across said output junctions, atransformer having a primary winding connected across said inputterminals, a pair of secondary low voltage windings in said transformereach connected to the electrode of one of said devices operating ascathode and supplying preheating current thereto, and an auxiliary highreactance secondary winding in said transformer connected between saidhigh input terminal and the common junction of the electrodes in saiddevices to supply an alterating voltage thereto whereby to ignite saiddevices, and grounded capacitive means extending the length of saiddevices in close proximity thereto.

6. An operating and starting circuit for a pair of electric dischargelamps comprising low and high input terminals for alternating currentenergization, a rectifiercapacitor bridge having a pair of branchesconnected across said input terminals, each branch including a rectifierand a capacitor connected in series, the junction points of therectifier and capacitor in each branch forming output junctions, autilization circuit comprising an inductance and terminals foraccommodating a pair of electric discharge lamps serially connectedacross said output junctions, a transformer having a primary Windingconnected across said input terminals, a pair of secondary low voltagewindings in said transformer each having terminals for connection to theelectrode of one of said lamps operating as cathode and supplyingpreheating current thereto, and an auxiliary high reactance secondarywinding in said transformer connected between said high input terminaland the common junction of the terminals for said serially connectedlamps to supply an alternating voltage thereto whereby to ignite saidlamps in the presence of grounded capacitive means extending along saidlamps in close proximity thereto.

7. An operating and starting circuit for a pair of electric dischargedevices comprising low and high input terminals for alternating currentenergization, a rectifiercapacitor bridge having a pair of branchesconnected across said input terminals, each branch including aninductor, a rectifier and a capacitor connected in series, therectifiers being poled for conduction in opposite directions in the twobranches, the junction points of the rectifier and capacitor in eachbranch forming output junctions, a utilization circuit comprising aninductance and a pair of electric discharge devices connected in seriesacross said output junctions, a transformer having a primary windingconnected across said input terminals, a pair of secondary low voltagewindings in said transformer each connected to the electrode of one ofsaid devices operating as cathode and supplying preheating currentthereto, and an auxiliary relatively high voltage high reactancesecondary winding in said transformer connected between said high inputterminal and the common junction of the electrodes in said devices tosupply an alternating voltage thereto whereby to ignite said devices,and grounded capacitive means extending the length of said devices inclose proximity thereto.

8. An operating and ballasting circuit fora pair of electric dischargedevices each having a pair of electrodes, comprising a pair of inputterminals for alternating current energization, a rectifier-capacitorbridge having a pair of branches connected across said input terminals,each branch including a rectifier and a capacitor con nected in series,the rectifiers being connected to one input terminal and poled forconduction in opposite directions, the capacitors being substantiallyequal in value and connected to the other input terminal, the junctionpoints of the rectifier and capacitor in each branch forming outputjunctions, a utilization circuit comprising an inductance and a pair ofelectric discharge devices connected in series across said outputjunctions, said utilization circuit having an impedance proportioned toachieve substantial transfer of energy to said discharge devices duringthe charging periods of said capacitors as well as during thedischarging periods, transforming means having a primary windingconnected across said input terminals, a pair of low voltage secondarywindings in said transformer each connected to the electrode of one ofsaid devices operating as a cathode and supplying pre heating currentthereto, an auxiliary high reactance and relatively low current capacitysecondary winding in said transformer, and a connection from saidauxiliary winding to the junction between the cathode of one lamp andthe anode of the other lamp, thereby providing to said junction an A.-C.voltage with respect to ground in order to ignite said devices.

9. An operating and starting circuit for a pair of electric dischargedevices comprising low and high input terminals for alternating currentenergization, a rectifiercapacitor bridge having a pair of branchesconnected across said input terminals, each branch including a rectifierand a capacitor connected in series, the junction points of therectifier and capacitor in each branch forming output junctions, autilization circuit comprising an inductance and a pair of electricdischarge devices connected in series across said output junctions, atransformer having a primary winding connected across said inputterminals, a pair of secondary low voltage windings in said transformereach connected to the electrode of one of said devices operating ascathode and supplying pre- 3 heating current thereto, and a highimpedance connected between said high input terminal and the commonjunction of the electrodes in said devices to supply an alterhatingvoltage thereto whereby to ignite said devices, and grounded capacitivemeans extending the length of said devices in close proximity thereto.

References Cited in the file of this patent UNITED STATES PATENTS GenuitJan. 23, 1962

1. AN OPERATING AND STARTING CIRCUIT FOR A PAIR OF ELECTRIC DISCHARGEDEVICES COMPRISING INPUT TERMINALS FOR ALTERNATING CURRENT ENERGIZATION,A RECTIFIER-CAPACITOR BRIDGE HAVING A PAIR OF BRANCHES CONNECTED ACROSSSAID INPUT TERMINALS, EACH BRANCH INCLUDING A RECTIFIER AND A CAPACITORCONNECTED IN SERIES, THE JUNCTION POINTS OF THE RECTIFIER AND CAPACITORIN EACH BRANCH FORMING OUTPUT JUNCTIONS, A UTILIZATION CIRCUITCOMPRISING A PAIR OF ELECTRIC DISCHARGE DEVICES CONNECTED IN SERIESACROSS SAID OUTPUT JUNCTIONS, AND HIGH IMPEDANCE MEANS SUPPLYING ANALTERNATING VOLTAGE TO THE COMMOM JUNCTION OF THE ELECTRODES IN SAIDDEVICES IN ORDER TO IGNITE THEM.